Double yolkers being incubated naturally?......

I have a breeding pair of pekin ducks and buff orpington. My buff drake has been breeding both females and vise versa with the pekin drake. My pekin hen lays an unusual amount of double yolkers. Now she is not a very broody girl but my buff is. To give her a good full clutch, I took the liberty of adding a few more eggs. She was happy to have them. About 6 of the eggs I gave her were double yolkers. I know this by the size of the eggs. I am wondering first what the chance of survival for twins is and two, how rare is it for my pekin to be laying double yolkers about twice a week. Would it have anything to do with her being breed buy both breeds drakes?

It's got nothing to do with the males, unless one of them carries genetics which produce double-yolker layers, and he's her father.

The double yolker trait is something usually culled or bred out of chickens and other poultry when it crops up in a breed. It seems to be related to breeding for high production with more than one egg a day. Some females don't have a long enough period of time between each egg's production and this leads to combined eggs.

As I mentioned it's culled out of most breeds whenever it shows up, and for good reason. It's highly heritable. Not only does it lead to females who run a much higher risk of dying due to being eggbound and other complications, but double yolkers have an extremely low incidence of producing even one live chick, and most often that chick will be weakly and fail to thrive or live to adulthood. Most double-yolker eggs fail to develop in the first place and those that do have other issues.

I've been there and done that with chickens and I will not breed any female who produces more than one double yolker, ever again; in fact I consider it a strike against them to ever produce one.

I understand the curiosity, and there are some threads about these forums detailing others' experiences. But it's basically guaranteed to lead to loss of life.